To be honest, it's not an incredibly important plot point. It shouldn't impact this RPG particularly (I doubt Rothax and co will be bothered if your character was trained by a 100-year old Z-Fighter) although by the start of the RPG, every original character has passed on, including those who were only 4 or 5 (such as Trunks/Goten) at the end of the Buu saga. That is just one thing I want to make clear.